Referring to FIG. 1, image sensors 10 typically include pixels 20 having a photosensitive area or photodiode 30 for capturing incident light and associated circuitry 40 adjacent the photosensitive area for processing and the like. In some cases, pixels 20 of an image sensor 10 are arranged asymmetrically to maximize the performance of the pixel while accommodating the associated circuitry 40. However, in this case, four of the pixels 20 typically form a regular grid pattern forming a supercell 50. Referring to FIG. 2, a microlens 60 is positioned spanning and spatially centered over the “photosensitive portion” of the pixels 20. Referring to FIG. 3, alternatively, microlenses 65 may be positioned spanning and centered over the entire “pixel” creating a regular array of microlenses.
Although the prior art arrangement of microlens 60 as in FIG. 2 is satisfactory, it includes drawbacks in that the microlens 60 is a small fraction of the area of the pixel, and therefore the photodiode 30 captures a small fraction of the incident light.
Still further, although the prior art arrangement of microlenses 65 (as in FIG. 3) over asymmetrically positioned pixels is satisfactory, they also include drawbacks. Referring to FIG. 4, as long as photodiodes 30 are symmetric with respect to the microlens 60 such as being centered in the pixel, then the performance of all pixels degrade in the same manner as the angle of the incident light is increased. As shown in FIG. 5, light passing (indicated by the dashed lines) through the microlenses 65 at certain angles is not directed onto the photodiode 30 causing undesirable degradation of the captured image when the photodiodes 30 are not arranged symmetrically with the microlens.
Consequently, a need exists for improved focusing of light on asymmetrical positioned pixels.